Ablation catheter with thermally mediated catheter body for mitigating blood coagulation and creating larger lesion

ABSTRACT

An ablation catheter is provided for ablating internal tissue of a patient. The catheter includes a distal end that is adapted to be inserted into a body cavity relative to a desired location therein (e.g., within the heart). An ablation electrode is connected relative to the distal end of the catheter for providing ablation energy to patient tissue. A heat sink is provided that is in thermal contact with the ablation electrode. The heat sink, in addition to being in thermal contact with the ablation electrode, is electrically isolated from the ablation electrode. This allows the heat sink to conduct heat away from the ablation electrode without dissipating electrical energy from the electrode. In this regard, the heat sink may prevent build-up of excess heat within the electrode that may result in blood coagulation and/or tissue charring.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/618,692, filed 29 Dec. 2006, which is hereby incorporated byreference as though fully set forth herein.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The invention generally relates to catheters for the ablation of humantissue. One use of such catheters is for ablation of cardiac tissue.More specifically, the invention relates to an ablation catheterincluding a body having an electrode at a distal end for ablatingtissue, as well as a thermally conductive heat sink that conducts heataway from the electrode and surrounding blood to reduce or preventcoagulation of the blood and/or tissue charring.

b. Background Art

Catheters have been in use for medical procedures for many years.Catheters can be used for medical procedures to examine, diagnose, andtreat while positioned at a specific location within the body that isotherwise inaccessible without more invasive procedures. During theseprocedures a catheter is inserted into a vessel near the surface of thebody and is guided to a specific location within the body forexamination, diagnosis, and treatment. For example, catheters can beused to convey an electrical stimulus to a selected location within thehuman body, e.g., for tissue ablation. In addition, catheters withsensing electrodes can be used to monitor various forms of electricalactivity in the human body, e.g., for electrical mapping.

Catheters are used increasingly for medical procedures involving thehuman heart. Typically, the catheter is inserted in an artery or vein inthe leg, neck, or arm of the patient and threaded, sometimes with theaid of a guide wire or introducer, through the vessels until a distaltip of the catheter reaches the desired location for the medicalprocedure in the heart. In the normal heart, contraction and relaxationof the heart muscle (myocardium) takes place in an organized fashion aselectro-chemical signals pass sequentially through the myocardium fromthe sinoatrial (SA) node, which comprises a bundle of unique cellsdisposed in the wall of the right atrium, to the atrioventricular (AV)node and then along a well-defined route into the left and rightventricles.

Sometimes abnormal rhythms occur in the heart, which are referred togenerally as arrhythmia. For example, a common arrhythmia isWolff-Parkinson-White syndrome (W-P-W). The cause of W-P-W is generallybelieved to be the existence of an anomalous conduction pathway orpathways that connect the atrial muscle tissue directly to theventricular muscle tissue, thus bypassing the normal conduction system.These pathways are usually located in the fibrous tissue that connectsthe atrium and the ventricle.

Other abnormal arrhythmias sometimes occur in the atria, which arereferred to as atrial arrhythmia. Three of the most common atrialarrhythmia are ectopic atrial tachycardia, atrial fibrillation, andatrial flutter. Atrial fibrillation can result in significant patientdiscomfort and even death because of a number of associated problems,including the following: an irregular heart rate, which causes patientdiscomfort and anxiety; loss of synchronous atrioventricularcontractions, which compromises cardiac hemodynamics, resulting invarying levels of congestive heart failure; and stasis of blood flow,which increases the likelihood of thromboembolism.

Efforts to alleviate these problems in the past have includedsignificant usage of pharmacological treatments. While pharmacologicaltreatments are sometimes effective, in some circumstances drug therapyhas had only limited effectiveness and is frequently plagued with sideeffects, such as dizziness, nausea, vision problems, and otherdifficulties.

An increasingly common medical procedure for the treatment of certaintypes of cardiac arrhythmia is catheter ablation. During conventionalcatheter ablation procedures, an energy source is placed in contact withcardiac tissue to heat the tissue and create a permanent scar or lesionthat is electrically inactive or noncontractile. During one procedure,the lesions are designed to interrupt existing conduction pathwayscommonly associated with arrhythmias within the heart. The particulararea for ablation depends on the type of underlying arrhythmia.

Ablation of a specific location within the heart requires the preciseplacement of the ablation catheter within the heart. Precise positioningof the ablation catheter is especially difficult because of thephysiology of the heart, particularly because the heart continues tobeat throughout the ablation procedures. Commonly, the choice ofplacement of the catheter is determined by a combination ofelectrophysiological guidance and fluoroscopy (placement of the catheterin relation to known features of the heart, which are marked byradiopaque diagnostic catheters that are placed in or at knownanatomical structures, such as the coronary sinus, high right atrium,and the right ventricle).

The ablation catheter produces lesions and electrically isolate orrender the tissue non-contractile at particular points in the cardiactissue by physical contact of the cardiac tissue with an electrode ofthe ablation catheter and application of energy. The lesion partially orcompletely blocks the stray electrical signals to lessen or eliminatearrhythmia.

The energy necessary to ablate cardiac tissue and create a permanentlesion can be provided from a number of different sources. Originally,direct current was utilized although laser, microwave, ultrasound, andother forms of energy have also been utilized to perform ablationprocedures. Because of problems associated with the use of DC current,however, radiofrequency (RF) has become the preferred source of energyfor ablation procedures.

In addition to radiofrequency ablation catheters, thermal ablationcatheters have been utilized. During thermal ablation procedures, aheating element, secured to the distal end of a catheter, heatsthermally conductive fluid, which fluid then contacts the human tissueto raise its temperature for a sufficient period of time to ablate thetissue.

Conventional ablation procedures utilize a single distal electrodesecured to the tip of an ablation catheter. Increasingly, however,cardiac ablation procedures utilize multiple electrodes affixed to thecatheter body. These ablation catheters often contain a distal tipelectrode and a plurality of ring electrodes. To form linear lesionswithin the heart using a conventional ablation tip electrode requiresthe utilization of procedures such as a “drag burn.” The term “linearlesion” as used herein means an elongate, continuous lesion, whetherstraight or curved, that blocks electrical conduction. During a “dragburn” procedure, while ablating energy is supplied to the tip electrode,the tip electrode is drawn across the tissue to be ablated, producing aline of ablation. Alternatively, a series of points of ablation areformed in a line created by moving the tip electrode incrementaldistances across the cardiac tissue.

The effectiveness of these procedures depends on a number of variablesincluding the position and contact pressure of the tip electrode of theablation catheter against the cardiac tissue, the time that the tipelectrode of the ablation catheter is placed against the tissue, theamount of coagulum that is generated as a result of heat generatedduring the ablation procedure, and other variables associated with abeating heart, especially an erratically beating heart. Unless anuninterrupted track of cardiac tissue is ablated, unablated tissue orincompletely ablated tissue may remain electrically active, permittingthe continuation of the stray circuit that causes the arrhythmia.Generally, it has been discovered that more efficient ablation may beachieved if a linear lesion of cardiac tissue is formed during a singleablation procedure.

During conventional ablation procedures, the ablating energy isdelivered directly to the cardiac tissue by an electrode on the catheterplaced against the surface of the tissue to raise the temperature of thetissue to be ablated. This rise in tissue temperature also causes a risein the temperature of blood surrounding the electrode, which oftenresults in the formation of coagulum on the electrode, which reduces theefficiency of the ablation electrode. Accordingly, it is desirable tomaintain the temperature of the electrode at a temperature that does notresult in the coagulation of surrounding blood. However, it will beappreciated that this desire is balanced with the need to provide enoughenergy to create a lesion (e.g., ablate tissue) of a desired depth.

The temperature of an electrode may vary over its length and isdependent upon the duration that energy is applied to the electrode. Forinstance, the distal tip of the electrode, which may be contact withpatient tissue, typically does not cause significant coagulationproblems for short duration (e.g., single location) ablation procedures.That is, for short procedures conductive transfer of energy from the tipof the electrode may keep the electrode tip below coagulationtemperatures. In contrast, proximal portions of the electrode, which aretypically in contact with patient fluid (e.g., blood), depend uponconvection to remove heat generated within the electrode and are apt tosee significant temperature increases even during short ablationprocedures. That is, the convective heat transfer with the surroundingblood alone may not be efficient enough to maintain the proximalportions of the electrode at a temperature that is below the coagulationtemperature of blood. Further, for longer duration procedures ormultiple single location procedures, heat may build-up throughout theelectrode, which may result in coagulation for the entire electrode aswell as the possibility of tissue charring.

One approach to lower catheter temperature and thereby reduce bloodcoagulation is to use ablation electrodes having an increased size. Suchlarge electrodes (e.g., 8 mm or 10 mm electrodes) provide an increasesurface area for convective heat transfer, which works to reduceelectrode temperature. However, such large electrodes also reducedelivered energy density and therefore require increased ablation energyto create a desired lesion as energy is dissipated through the increasedsurface area to surrounding fluid.

To achieve efficient and effective ablation, coagulation of blood thatis commonly associated with conventional ablation catheters should beavoided. This coagulation problem can be especially significant whenlinear ablation lesions or tracks are produced because such linearablation procedures conventionally take more time than ablationprocedures ablating only a single location and can result in heat buildup within the electrode.

BRIEF SUMMARY OF THE INVENTION

It is desirable to prevent excessive heat build up within an electrodewithout necessarily having to increase the size of the electrode, whichcan lead to increased energy dissipation. In this regard, the inventorshave recognized that it is desirable to increase the surface area of anelectrode for convective cooling. However, the inventors have alsorecognized that an increase in the convective cooling surface area of anelectrode need not increase the electrically conductive surface area ofthe electrode and therefore increase the energy dissipated by theelectrode. That is, the inventors have recognized that use of athermally conductive and electrically isolative heat sink that is inthermal contact with the electrode may provide improved cooling for theelectrode without significantly altering the operating parameters of theelectrode.

According to one aspect, an ablation catheter is provided for ablatinginternal tissue of a patient. The catheter includes a body having aproximal portion and a distal end. The distal end is adapted to beinserted into a body cavity relative to a desired location therein(e.g., within the heart). An ablation electrode is connected relative tothe distal end of the catheter for providing ablation energy to patienttissue. A heat sink is in thermal contact with the ablation electrode.The heat sink, although in thermal contact with the ablation electrode,is electrically insulated (e.g., substantially electrically isolated)from the ablation electrode. This allows the heat sink to conduct heataway from the ablation electrode without dissipating electrical energyfrom the electrode. In this regard, the heat sink may prevent build-upof excess heat within the electrode that may result in blood coagulationand/or tissue charring.

Generally, the heat sink is formed of a thermally conductive andelectrically resistive element that may be in direct physical contactwith the ablation electrode. Alternatively, the heat sink and electrodemay be interconnected by an intermediate member, such as, for example, athermally conductive adhesive. To provide desired conductive heattransfer from the ablation electrode, the heat sink may have a thermalconductivity in excess of about 0.01 watts/cm Kelvin. In a furtherembodiment, the heat sink may have a thermal conductivity of greaterthan about 0.1 watts/cm Kelvin. In a yet further embodiment, the heatsink may have a thermal conductivity of greater than 1.0 watts/cmKelvin. In order to be electrically insulated from the ablationelectrode, the heat sink may have an electrical resistivity thatprevents most or all electrical conduction therein. In this regard, theheat sink may have an electrical resistivity in excess of that of theablation electrode and/or patient tissue. In another arrangement, theelectrical resistivity is greater than about 1.0×10³ ohm cm. In thisregard, the heat sink may be any material that exhibits high electricalresistivity in conjunction with desired thermal conductivity.

Some non-limiting examples of materials that may be utilized as a heatsink with the catheter include diamond, diamond-like carbon, aluminumnitride, boron nitride, thermoconductive epoxies and thermal polymers(i.e., thermoconductive polymers). Such polymers may include conductivemedia within their structure. In the latter regard, use of athermoconductive polymer may allow the distal end of the catheter bodyto form the heat sink. That is, the catheter body may be formed of apolymer/plastic having enhanced thermal conductivity properties.

In other arrangements, the heat sink may be separately formed from theablation electrode and/or the distal end of the catheter body. In sucharrangements, the heat sink may be attached to the ablation electrodeand/or the catheter body in any appropriate manner. In one arrangement,the heat sink is disposed between the ablation electrode and the distalend of the catheter body. In such an arrangement, the heat sink mayinclude one or more internal passageways or lumens that permit internalaccess between the ablation electrode and the distal end of the catheterbody. Such internal passageways may be aligned with lumens in thecatheter body and/or ablation electrode such that, for example, fluidmay be provided from the catheter body, through the heat sink andthrough the electrode. Additionally, electrical wiring and/or guidewires may extend from the catheter body, through the heat sink and tothe electrode. Where the electrode, heat sink and catheter body aredisposed in a series, outside surfaces of these components may beconformal or otherwise share a common cross-sectional shape.

In another arrangement, the heat sink may be attached to the electrodeover a portion or all of its length. In such an arrangement, theelectrode may have a distal tip and a proximal end (e.g., for attachmentto the catheter body), and the heat sink may be attached to a portion ofthe length of the electrode. In another arrangement, the heat sink mayextend over essentially the entire length of one surface of theelectrode.

In another aspect, an ablation electrode is provided that has a portionof the active surface of the electrode covered by an electricallyinsulative material. This electrically insulative material or electricalinsulator prevents dissipation of energy from the electrode tosurrounding media (e.g., tissue and/or fluid). In such an arrangement,the size of the electrode may be increased to provide additionalconvective cooling. The electric insulator may prevent the dissipationof energy from a portion of the outside surface of the electrode andthereby reduce the energy required by the electrode for an ablationprocedure. Likewise, additional energy may be available for an ablationprocedure.

In one arrangement, the electrically insulative material is applied toan outside surface of the electrode. Such material may be applied as,for example, a film or wrap (e.g., tape) that may extend over or arounda portion of the electrode that is not intended to contact patienttissue. Such an electrically insulative material may be thin enough topermit thermal conductivity from the electrode to surrounding media tomaintain a desired temperature within the electrode. In anotherarrangement, the electrically insulative material may also be thermallyconductive to enhance heat transfer from the electrode to surroundingmaterial. In one arrangement, a heat shrink tape may be applied to aproximal portion of an electrode while the distal tip of the electroderemains uncovered such that it may be utilized to apply ablation energyto tissue.

The foregoing and other aspects, features, details, utilities, andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is one embodiment of an ablation catheter in accordance with thepresent disclosure.

FIGS. 2A and 2B illustrate energy dissipation and thermal conductivity,respectively, in one embodiment of an ablation electrode.

FIGS. 3A and 3B illustrate energy dissipation and thermal conductivity,respectively, in a first embodiment of an ablation electrode inaccordance with the present disclosure.

FIGS. 4A and 4B illustrate energy dissipation and thermal conductivity,respectively, in a second embodiment of an ablation electrode inaccordance with the present disclosure.

FIGS. 5A and 5B illustrate energy dissipation and thermal conductivity,respectively, in a third embodiment of an ablation electrode inaccordance with the present disclosure.

FIG. 6A illustrates a perspective view of a fourth embodiment of anablation electrode in accordance with the present disclosure.

FIGS. 6B and 6C illustrate energy dissipation and thermal conductivity,respectively, of the ablation electrode of FIG. 6A

FIGS. 7A and 7B illustrate perspective and cross-sectional views,respectively of a fifth embodiment of an ablation electrode inaccordance with the present disclosure.

FIG. 8 is a graph illustrating power of different electrodeconfigurations under temperature controlled ablation.

FIG. 9 is a graph illustrating lesion depths for the different electrodeconfigurations of FIG. 8.

FIG. 10 is a graph illustrating lesion depth of different electrodeconfigurations under power controlled ablation.

FIG. 11 is a graph illustrating temperatures for different electrodeconfigurations for the power controlled ablation of FIG. 10.

FIGS. 12A, 12B and 12C are graphs of temperature distribution in tissuefor different electrode configurations.

FIG. 13 is a table of the temperature distributions of FIGS. 12A, 12Band 12C.

DETAILED DESCRIPTION OF THE INVENTION

The ablation catheter 10 of the present invention as shown in FIG. 1 iscomprised of a catheter body 12 with a proximal end 14 and a distal end16, at least one lumen (not shown) extending lengthwise substantiallythrough the catheter body 12, and an electrode (22), secured relative tothe distal end 16 of catheter body. In the present embodiment, a heatsink element 40 is disposed between the distal end 16 of the catheterbody 12 and the electrode, as will be more fully discussed herein. Thecatheter body 12 may be a conventional elongated catheter made ofmaterials suitable for use in humans, such as nonconductive polymers.Exemplary polymers used for the production of the catheter body includethose well known in the art such as thermoplastic polyurethanes,thermoplastic elastomers (polyamide-based, polyester-based, olefinic andstyrenic), polyolefins, nylons, polytetrafluoroethylene, polyvinylidenefluoride, and fluorinated ethylene propylene polymers and otherconventional materials.

The length of the catheter 10 may be of any appropriate length typicallybeing between about 50 cm to about 150 cm (20 to 60 in.). The diameterof the catheter 10 is within ranges well known in the industry,generally, from about 4 to 16 French and more preferably from about 6 to8 French (1 French equals ⅓ of a millimeter (0.013 in.)).

The catheter body 12 generally contains one or more lumens extendingthrough the catheter body 12 from its proximal end to near its distalend. Typically, a sufficient number of lumens are present in thecatheter body 12 to accommodate power and control wires for theelectrode 22. Lumens may also accommodate, without limitation, wires forthermo sensing devices, such as thermocouples, sensing electrodes and/orelectrodes used to gage contact with conductive media or tissue. Inaddition, in the present embodiment, a fluid irrigation lumen 36 isprovided that may be attached to a fluid source to provide, for example,saline through the catheter body 12 to the electrode 22. In oneembodiment, such lumens may have a diameter of at least about 0.2 mm(0.008 in.) and more typically from about 0.3 mm (0.01 in.) to about 1.0mm (0.04 in.).

FIGS. 2A and 2B illustrate electrical current density and thermalconductivity, respectively, of an ablation electrode 22 of an ablationcatheter 10 where the ablation electrode 22 (which may be formed ofplatinum and/or iridium) is attached to the distal end 16 of a catheterbody 12. In this regard, the electrically conductive electrode 22 isattached to the substantially insulative (i.e., electrically insulative)distal end 16 of the typically plastic catheter body 12 and is utilizedto create a lesion 8 in patient tissue. FIG. 2A illustrates theelectrical current density as represented by arrows 26 (i.e., current26). As will be appreciated, such current density results in Jouleheating (i.e., increase in temperature of a conductor as a result ofresistance to an electrical current flowing through the conductor)within the electrode 22. Such current density and resulting Jouleheating is highest at the interface of the electrode 22 and catheterbody 12 due to the large difference of electrical resistivity betweenthe highly conductive electrode 22 and the low conductivity catheterbody 12.

Furthermore, the distal end of the plastic catheter body 12 has a lowcoefficient of thermal conductivity and therefore allow little thermalconduction, as represented by the thick arrows which define heat flowpaths 28, from the proximal end of the electrode 22 to the catheter body12. See FIG. 2B. Accordingly, heat generated within the electrode 22near the interface may build up over time and create a “hot spot” 30around the electrode/catheter body interface. This hot spot 30 may havea temperature that is considerably higher than surrounding regions andmay heat surrounding blood, which may lead to coagulation.

The heat build up at the electrode/catheter body interface is due inpart to the lack of a heat transfer path that is sufficient to transferheat out of the electrode 22 at a rate which heat is generated withinthe electrode 22. In this regard, it is noted that the proximal end ofthe electrode 22 that interfaces with the catheter body 12 dependsprimarily upon convective heat transfer (e.g., with surrounding blood)to remove heat. Further, depending on the location of the heart chamberand the catheter orientation, blood flow around the proximal end of theelectrode 22 may be limited further reducing the effectiveness of theconvective heat transfer at the proximal end of the electrode 22. Forinstance, when an electrode is disposed under the tricuspid valve ormitral valve, there may be little or no blood flow such that there islittle convective heat transfer. Accordingly, the electrode/catheterbody interface can reach a temperature that causes a hot spot in thesurrounding blood, blood coagulation and/or catheter damage.

In contrast, the distal tip of the electrode 22 is in thermal andelectrical conduct with myocardium tissue that provides a conductiveheat transfer path that allows for increased heat dissipation from thetip of the electrode 22 (i.e., in relation to the proximal end of theelectrode 22). That is, due to the contact with the tissue, heat may beconductively transferred from the tip of the electrode 22 therebypreventing or reducing heat build up within the tip of the electrode 22.Accordingly, the tip of the electrode may not reach coagulationtemperatures or may take longer to reach coagulation temperatures.

To reduce or substantially eliminate the temperature build up at theinterface between the electrically conductive electrode 22 and theelectrically and thermally insulative catheter body 12, the electrodeembodiment of FIG. 3A and 3B disposes a heat sink 40 between theelectrode 22 and the distal end 16 of the catheter body 12. This heatsink 40 is an electrically insulative (e.g., an electrical isolator) butthermally conductive element. As it is electrically insulative, theelectrical field within the electrode 22 as shown in FIG. 3A behavessubstantially the same as the electrical field within the ablationelectrode as shown in FIG. 2A. In this regard, little or no current 26flows into the electrically insulative heat sink 40. Accordingly, thereis little or no joule heating in the heat sink 40. However, as the heatsink 40 is thermally conductive, heat is extracted from the proximal endof the electrode 22 thereby reducing and/or preventing heat build up inthe electrode 22. This reduces or prevents the generation of a hot spot30 in the surrounding blood. That is, heat is conducted away from theproximal end of the electrode 22 and distributed throughout the heatsink 40, which provides additional surface area for dissipating theheat. That is, the combined surface area of the heat sink 40 andelectrode 22 allows for more readily dissipating heat from the electrode22 to reduce or prevent heat build up and/or the generation of a hotspot 30. That is, the combined surface area improves convective heattransfer from the proximal end of the electrode. Further, the heat sinkmay absorb heat from surrounding blood to help avoid coagulation.

In addition to reducing the temperature of the proximal end of theelectrode 22, the heat sink 40 may also reduce the overall temperatureof the electrode 22. It will be appreciated that for single locationablation procedures, energy may be applied to the electrode 22 for shortdurations. Accordingly, contact with the tissue and the short durationof applied energy typically prevents heat build up in the tip of theelectrode 22. However, in other ablation procedures such as drag burnprocedures, energy may be applied to the electrode 22 for longerdurations. These longer duration procedures may result in heat build upthroughout the entire electrode 22 including the portion of theelectrode in contact with tissue. Such heat build up can result incoagulation of surrounding blood as well as tissue charring (e.g.,myocardium charring). Accordingly, use of the heat sink 40 may allow forreducing the overall temperature of the electrode 22 including thetemperature at the electrode/tissue interface. This can reduce orprevent coagulation and/or tissue charring. However, it will be notedthat this electrode temperature reduction (i.e., electrode cooling) onlyaffects the electrode tissue interface and does not adversely affect thethermal conduction inside the tissue. In this regard, temperatureswithin the tissue may be increased to a desired temperature to create alesion 8 having a desired depth.

It will be appreciated that any suitable electrically insulative andthermally conductive material may be utilized as a heat sink. As shown,Table 1 illustrates a non-limiting group of materials that may beutilized as an electrically insulative heat sink. Specifically, Table 1shows the resistivity and thermal conductivity of various materials.Also included in Table 1 for purposes of comparison are the resistivityand thermal conductivity of tissue, blood, polyurethane (e.g., anon-conductive catheter body), and a platinum/iridium electrode.

TABLE 1 p (Ω · cm) k (W/cm · K) Tissue 200 0.0055 Blood 150 0.0055Electrode (Pt/Ir) 2.5 · 10⁻⁵ 0.7 Polyurethane >10⁷ 0.00026Diamond/Diamond- >10⁷ 20 like Carbon Aluminum Nitride   10⁷ 3.7 BoronNitride >10⁷ 13 (theory) CoolPoly >10⁷ 0.1 Silicone 0.0025 1.5 ThermalEpoxy >10⁷ 0.01

As shown, materials suitable for use as an electrically insulative andthermally conductive heat sink include diamond/cubic zirconium,diamond-like carbon, ceramics, such as aluminum nitride, boron nitride,silicon carbide and alumina. Each of these materials provides electricalresistivity in conjunction with thermal conductivity. That is, thesematerials typically exhibit resistivity that is several orders ofmagnitude greater than tissue or blood while also having a thermalconductivity that is at least an order of magnitude greater than tissueor blood.

FIGS. 3A, 3B and 4-7B illustrate various configurations of a distal end16 of an ablation catheter including an electrode 22 and an electricallyinsulative thermal heat sink 40. As shown in FIG. 3A, the heat sink 40may be formed as a substantially solid piece that is attached to theproximal portion of the electrode 22 and to the distal end 16 of thecatheter body 12. In this regard, the electrode 22 and heat sink 40 maybe disposed in series. In such an arrangement, the outside surfaces ofthese components 22, 40 may be conformal (e.g., cylindrical) and/or maymatch the outside surface of the catheter body 12. As will beappreciated, in such an arrangement the solid heat sink 40 may includean internal passageway/lumen to allow for electrical and or fluidconnections between the electrode and the distal end of the catheterbody 12. Further, such a lumen may allow for a guide wire to extendthrough the heat sink 40 to the electrode 22.

In another arrangement, shown in FIG. 4A, an electrically insulativeheat sink is formed as a coating or casing 42 that is dispose about anoutside portion of the electrode 22 and/or catheter body 12. Such acasing 42 may be applied as a tape or film or as a rigid cylinderapplied to an outside surface of the electrode 22 and/or catheter body12. It will be noted that such a casing or coating may be applied toexisting electrodes to improve their functional qualities. For instance,larger/longer electrodes have previously been utilized to increase theconvective area of the electrode and thereby reduce the temperature ofthe electrode. For instance, FIGS. 4A and 4B illustrates an 8 mmelectrode whereas FIGS. 3A and 3B illustrates a 4 mm electrode. Thelarger electrode of FIGS. 4A and 4B provides a larger conductive surfacearea that allows for reducing the temperature of the electrode duringoperation. However, the larger conductive surface area results indissipation of ablation power into the surrounding fluid (e.g., salineor blood). See FIG. 4B. Accordingly, such larger/longer electrodes haverequired increased ablation power.

By providing an electrically insulative casing or coating 42 about aproximal portion of the electrode 22 (See FIG. 4A), energy dissipationfrom the proximal portion of the electrode may be reduced orsubstantially eliminated. Of note, embodiments where an electricallyinsulative casing or coating is applied to a proximal portion of anelectrode, the casing or coating need not have a high coefficient ofthermal conductivity as long as the casing or coating is thin enoughsuch that heat can easily dissipate through the casing/coating. In onearrangement, a heat shrink tape or tube may be applied around a proximalportion of an electrode. Such a heat shrink tape is typically thinenough to allow for ready transfer of heat while electricallysubstantially isolating a proximal portion of the electrode.

FIGS. 5A and 5B illustrate a third embodiment of an electrode having athermally conductive heat sink. In the embodiment of FIGS. 5A and 5B,the distal end 16 of the catheter body 12 forms a heat sink. In thisregard, all or at least the distal portion 16, of the catheter body 12is formed of thermally conductive compound. For instance, a thermallyconductive polymer or plastic such as Coolpoly® from Cool Polymers, Inc.of 333 Strawberry Field Rd. Warwick, R.I. 02886, may be utilized. Insuch an arrangement, the thermally conductive catheter body 12 mayprovide insulation of electrical current 26 between the electrode 22 andthe catheter body 12 (See FIG. 5A) to prevent diversion of ablationenergy while also providing a thermal conduction or heat flow path 28(See FIG. 5B) to dissipate heat generated within the electrode 22.Again, such thermal conduction may prevent heat build-up in theelectrode 22 and/or reduce or prevent the generation of a hot spot 30 insurrounding fluid.

FIGS. 6A, 6B and 6C illustrate another embodiment of an ablationelectrode 22 incorporating an electrically insulative thermal heat sink40. As shown, the heat sink 40 is disposed in parallel with theelectrode 22. More specifically, in this particular embodiment both theelectrode 22 and heat sink 40 form a half-cylinders that areinterconnected along their axial length. In such an arrangement, theelectrode 22 may be placed in contact with patient tissue (e.g.,myocardium) in order to focus energy (i.e., current 26) into the tissueto create a lesion 8. See FIG. 6B. In such an arrangement, the heat sink40 is exposed to blood for thermal convection. Again, the heat sink 40provides a heat flow path 28 for removing heat from the electrode 22.According, thermal conduction into the heat sink reduces temperatureover the length of the ablation electrode. In such an arrangement, theoverall length of the electrode may be sufficient to create linearlesions, for example, for AFL or AFIB ablation procedures.

FIGS. 7A and 7B illustrate another embodiment of an ablation electrodethat utilizes an electrically insulative and thermally conductive heatsink 40. As shown, the ablation electrode 22 is again attached thedistal end 16 of a catheter body 12 and a thermally conductive andelectrically insulative heat sink 40 is disposed between the electrode22 and the catheter body 12. Additionally, the catheter body 12, heatsink 40 and electrode 22 each include common internal passageways 44.These passageways 44 are adapted to carry a liquid coolant (e.g.,saline) from the proximal end of the catheter through the distal tip ofthe electrode 22. In this regard, tissue contacted by electrode 22 maybe bathed in coolant/saline during an ablation procedure. As will beappreciated, use liquid coolant passing through the electrode 22 mayhelp control the temperature of the electrode 22.

Further, as shown in the cross-sectional view of FIG. 7B, it may bedesirable to electrically insulate or isolate the coolant passageway 44from the electrode 22. In this regard, a thermally conductive andelectrically insulative barrier 46 (e.g., tube or cylinder) may beutilized to line the passageway 44. Such a barrier 46 may electricallyisolate the passageway 44 from the electrode and or a conductive coil 48that provides electrical energy to the electrode 22, while stillpermitting heat exchange between coolant passing through the passageway44 and electrode 22. In this regard, coolant passing through thepassageway 44 may provide cooling for the electrode 22 withoutdissipating energy from the electrode 22.

FIGS. 8-11 graphically illustrate lesion depth, power, cathetertemperature, and differences between the electrode of FIGS. 3A and 3Bincorporating the heat sink 40, the larger electrode of FIG. 4Aincorporating an electrically insulative casing/coating 42 and thelarger electrode of FIG. 4B without a casing/coating or heat sink.Respectively, these electrodes are referred to as a 4 mm electrode, a 8mm coated electrode and a 8 mm standard electrode. It will beappreciated that these sizes are presented by way of example and not oflimitation of the present disclosure.

FIG. 8 illustrates the power required by each of the electrodes tomaintain a 75 degree Celsius temperature. As shown, the 4 mm electroderequires the least power. Of particular note, the 8 mm coated electroderequires less than one-half the power of the 8 mm standard electrode.That is, the casing/coating 42 significantly reduces or eliminates theenergy dissipation from the coated portion of the electrode.Accordingly, as less power is dissipated into the surrounding fluid,more energy may be available to form a lesion within the tissue.

FIG. 9 illustrates the lesion depth of the 4 mm electrode, the 8 mmcoated electrode and 8 mm standard electrode. As shown, the 8 mmstandard electrode produces the deepest lesion. Specifically, the 8 mmuncoated electrode lesion is approximately 15% deeper than the lesioncreated by the 8 mm coated electrode. However, it will be appreciatedthat the deeper lesion was produced using approximately twice the powerof the 8 mm coated electrode. Accordingly, if a 8 mm coated electrode isutilized, such additional power would be available to create a deeperlesion. This is also true for the 4 mm electrode incorporating the heatsink.

FIGS. 10 and 11 illustrate catheter temperature and lesion depth undercontrolled power ablation. That is, in response to a fixed power levelbeing applied to the electrode, the depth of the lesion is measured andthe corresponding temperature of the electrode is measured. As shown inFIG. 10, the depth of the lesion created by an applied power of 10 wattsis substantially the same for the 4 mm electrode of FIG. 3A and the 8 mmcoated electrode of FIG. 4A. The depth of the lesion is slightly greaterfor the 8 mm coated electrode for an applied power of 15 watts. Ineither case, the depth of the lesion of the 4 mm electrode using theheat sink and the 8 mm coated electrode is significantly greater thanthat of the 8 mm standard electrode. For instance, lesion depths of the4 mm electrode using a heat sink and 8 mm coated electrode are betweenabout two and three times deeper than the lesion depth of the 8 mmstandard electrode. This is due in part to the reduced dissipation ofenergy into surrounding media (e.g., blood). That is, the standardelectrode dissipates energy into surrounding fluid that may otherwise beutilized to generate a lesion. Use of either an electrode with a heatsink or a coated electrode reduces such energy dissipation.

FIG. 11 illustrates the catheter temperature for the 4 mm, 8 mm coatedand 8 mm standard electrode at different power levels. As shown, the 4mm electrode using the heat sink and the 8 mm coated electrode reachhigher temperatures than the 8 mm standard electrode. However, thetemperatures of the 4 mm electrode using the heat sink and the 8 mmcoated electrode may be maintained within acceptable limits whileproviding significant improvements in lesion depth as noted in relationto FIG. 10.

FIGS. 12A, 12B and 12C illustrate temperature distribution withinpatient tissue contacted by an electrode 22 under identical operatingconditions. Specifically, FIG. 12A illustrates the temperaturedistribution of an electrode 22 and surrounding tissue for an electrodewithout a heat sink (e.g., as shown in FIG. 2A) where the proximal endof the electrode 22 contacts a thermally and electrically insulativeplastic catheter body 12. FIG. 12B illustrates the temperaturedistribution of an electrode and surrounding tissue for an electrodethat utilizes a thermally conductive catheter body 12 (e.g., a thermalpolymer embodiment as shown in FIG. 5A). FIG. 12C illustratestemperature distribution of an electrode and surrounding tissue for anelectrode that utilizes a heat sink connected to its proximal end (e.g.,as shown in FIG. 2A).

Results of the three temperature distributions are tabulated in FIG. 13.As illustrated, the electrode or ‘plastic’ embodiment of FIG. 12Aresults in a maximum tissue temperature of approximately 95 degreesCelsius, a maximum electrode temperature of approximately 85 degreesCelsius and a 5.2 mm lesion depth. In contrast, the thermal polymerembodiment of 12B results in a maximum temperature of approximately 84degrees Celsius of the tissue, a maximum electrode temperature ofapproximately 70 degrees Celsius and a 5 mm lesion depth. Finally, theembodiment of 12C utilizing the heat sink, which in this embodimentcomprises an aluminum nitrate heat sink, results in a maximum tissuetemperature of approximately 74 degrees Celsius, a maximum electrodetemperature of approximately 56 degrees Celsius and a lesion depth of4.9 mm. As shown, use of a thermally conductive catheter or a heat sinksignificantly reduces the tissue temperature and electrode temperaturewhile minimally affecting the lesion depth. As will be appreciated, thismay prevent or eliminate tissue charring during ablation procedures.

In addition to reducing the likelihood of tissue charring, it will beappreciated that the lowered electrode and tissue temperatures mayallows for the provision of additional power to the electrode. Suchadditional power may be utilized to create lesions having increaseddepth without increasing electrode and/or tissue temperatures beyonddesired thresholds.

Although five embodiments of this invention have been described abovewith a certain degree of particularity, those skilled in the art couldmake numerous alterations to the disclosed embodiments without departingfrom the spirit or scope of this invention. For example, it will beappreciated that a catheter may include multiple electrodes and/ormultiple heat sinks Further, it will be recognized that all directionalreferences (e.g., upper, lower, upward, downward, left, right, leftward,rightward, top, bottom, above, below, vertical, horizontal, clockwise,and counterclockwise) are only used for identification purposes to aidthe reader's understanding of the present invention, and do not createlimitations, particularly as to the position, orientation, or use of theinvention. Joinder references (e.g., attached, coupled, connected, andthe like) are to be construed broadly and may include intermediatemembers between a connection of elements and relative movement betweenelements. As such, joinder references do not necessarily infer that twoelements are directly connected and in fixed relation to each other. Itis intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative onlyand not limiting. Changes in detail or structure may be made withoutdeparting from the spirit of the invention as defined in the appendedclaims.

1-24. (canceled)
 25. An ablation catheter, comprising: a catheter body,the catheter body comprising a proximal portion and a distal portion,the distal portion being adapted to be inserted into a body cavity; anablation electrode connected relative to the distal portion of thecatheter body, wherein said ablation electrode forms a first portion ofan exterior surface of the distal portion of said catheter body; and aheat sink connected relative to the distal portion of the catheter body,wherein said heat sink forms a second portion of an exterior surface ofthe distal portion of said catheter body, said heat sink being inthermal communication with the ablation electrode and being electricallyinsulated from the ablation electrode.
 26. The catheter of claim 25,wherein the heat sink comprises a thermally conductive and electricallyresistive element.
 27. The catheter of claim 26, wherein the heat sinkhas an electrical resistivity of at least 1.0×103 ohm centimeters. 28.The catheter of claim 25, wherein the heat sink has a thermalconductivity of at least 0.01 watts per centimeter Kelvin.
 29. Thecatheter of claim 25, wherein the distal portion of the catheter bodyforms the heat sink.
 30. The catheter of claim 29, wherein at least thedistal portion of the catheter body comprises a thermally conductivepolymer.
 31. The catheter of claim 25, wherein the heat sink is disposedbetween the ablation electrode and the distal portion of the catheterbody, wherein the heat sink physically separates the electrode from thedistal portion of the catheter body.
 32. The catheter of claim 31,wherein the heat sink further comprises an internal passageway extendingbetween the ablation electrode and the distal portion of the catheterbody.
 33. The catheter of claim 32, wherein the ablation electrodefurther comprises an internal passageway in communication with theinternal passageway of the heat sink, wherein the internal passagewaysare adapted to receive fluid from the distal portion of the catheterbody.
 34. The catheter of claim 33, wherein the catheter body furthercomprises at least one lumen for providing a fluid flow to the internalpassageway of the heat sink.
 35. The catheter of claim 31, wherein theablation electrode and the heat sink have a common cross-sectionalprofile.
 36. The catheter of claim 25, wherein the ablation electrodeextends between a proximal electrode end and a distal electrode end andwherein the heat sink is in thermal contact with the ablation electrodeover a portion of the length of the ablation electrode between theproximal and distal electrode ends.
 37. The catheter of claim 36,wherein the heat sink is in thermal contact over substantially theentire length of the ablation electrode.
 38. The catheter of claim 25,wherein the ablation electrode comprises a plurality of ablationelectrodes, wherein said plurality of ablation electrodes form the firstportion of the exterior surface of the distal portion of said catheterbody, and wherein said heat sink is in thermal communication with theplurality of ablation electrodes and is electrically insulated from theplurality of ablation electrodes.
 39. An ablation catheter, comprising:a catheter body, the catheter body comprising a proximal portion and adistal portion; an ablation electrode; and a thermally conductive heatsink positioned in thermal communication with the ablation electrode andelectrically insulated from the ablation electrode, said thermallyconductive heat sink having a first end coupled to the distal portion ofthe catheter body and a second end that supports the ablation electrode,wherein said thermally conductive heat sink substantially isolates saidablation electrode from the distal portion of the catheter body.
 40. Thecatheter of claim 39, wherein said thermally conductive heat sinkcomprises an electrically resistive element.
 41. The catheter of claim40, wherein the thermally conductive heat sink has an electricalresistivity of at least 1.0×103 ohm centimeters.
 42. The catheter ofclaim 39, wherein the ablation electrode has a distal tip for contactingtissue and the heat sink is connected to a proximal end of the ablationelectrode.
 43. The catheter of claim 39, wherein said ablation electrodeis connected relative to the distal portion of the catheter body andforms a first portion of an exterior surface of the distal portion ofsaid catheter body and said thermally conductive heat sink is connectedrelative to the distal portion of the catheter body and forms a secondportion of an exterior surface of the distal portion of said catheterbody.
 44. The catheter of claim 39, wherein the thermally conductiveheat sink has a thermal conductivity of at least 0.05 watts percentimeter Kelvin.